The present invention relates to a water-cooled winding for an electromagnetic stirrer.
Since an electromagnetic stirrer is set in a narrow place, the stirrer should be designed to have a compact size. Furthermore, since a large current is often applied to the stirrer, the superheated portion of the electromagneitc stirrer, such as a winding, that is, a coil, should be cooled. In case of an electromagneitc stirrer having a coil to be air-cooled, a maximum current density of about 3 to about 5 A/mm.sup.2 can be used, but if the maximum current density exceeds 10 A/mm.sup.2, this electromagnetic stirrer cannot be used. Accordingly, in such a case, an electromagnetic stirrer having a coil to be water-cooled is used.
FIG. 1 is a sectional view of a winding portion of a conventional water-cooled electromagnetic stirrer, and FIG. 2 is an enlarged sectional view of a coil used in the stirrer shown in FIG. 1.
Referring to FIG. 1, a winding-constituting coil 1 comprising a wire wound in an ellipsoidal shape has an iron core 2 inserted therein, and the coil 1 is fixed to the iron core 2 through a wedge 3 and a spacer 4. The coil 1 fixed to the iron core 2 is impregnated with a resin integrally with the iron core 2 for insulation.
In FIG. 2, reference numeral 5 represents a conductor having a predetermined number of turns, for example, a flat type wire. A polyimide film or other film is wound in semi-lap-winding in several turns on the surface of the conductor 5 to form a turn insulation layer 6. For example, a glass tape is wound in 2.5-lap winding on the upper layer of the turn insulation layer 6 along the entire conductor 5 to form a main insulation layer 7.
In case of the conventional water-cooled electromagnetic stirrer, it is indispensable that the turn insulation layer 6 should be composed of an insulating material having a good water resistance and should also exert the function of main insulator layer 7. The main insulation layer 7 takes a role of bundling respective conductors 5 and assists the function of the water-resistant insulation of which the turn insulation layer 6 possesses.
In the winding of the conventional water-cooled electromagnetic stirrer described above, the turn insulation layer 6 is required to be water-resistant, and is required to have a role of electric insulation not only between every two adjacent coil turns but also in the entire coil turns (main insulation). Accordingly, the thickness of the turn insulation layer 6 is increased and the size of the coiled winding as a whole is increased. Moreover, since a flat type wire having the turn insulation layer 6 formed by winding a film in multiple plys is subjected to a coiling process, the turn insulation layer 6 is readily degraded during the processing and the life of the coil 1 is shortened. If a flat type wire is first subjected to the coiling processing and a turn insulation layer 6 is then formed, the operation is extremely complicated and requires many steps, and the production becomes economically disadvantagenous.